Molded plastic parts have becoming increasingly popular, due at least in significant part to their low production cost. Hence, often, one or more components of an assembly are formed of molded plastic. In assembling a final product it is often necessary to fasten the molded plastic parts to other components to produce the final product.
The present invention is of particular use to molders of plastic parts, such as molded plastic shells or bodies, who desire to attach another plastic member to the body and/or to assemblers who desire to attach a first plastic material member to a second plastic material member. The present invention will be described in connection with an illustrated embodiment wherein a hollow, plastic container e.g., made of polyethylene terephthalate (PET) plastic has a thin wall to which it is desired to secure a separate handle e.g., of PET or of a polycarbonate plastic in the shape of a loop, but is not limited to these examples. When lifting or pouring liquid from the container, the user may insert his fingers into the loop and grip the outer portion of the loop. When making such containers it may be desirable to be able to use handles of a different thickness or a shape that would be difficult to mold integrally with the container or of a different material than the container material. Some plastics such as PET are most desirable for containers, such as bottles or drinking cups, because of its clarity, crystalline appearance, toughness, etc.; but PET may be a difficult material to which to attach handles when using conventional attaching techniques. The present invention is not limited to PET material because for many other plastic objects, such as for the PET container piece, it is desired to provide a good attachment between the first plastic piece and a second plastic piece such as a handle. While ultrasonic welding of plastic pieces together is well known, the piece shapes are not specifically designed to direct or concentrate the ultrasonic energy to achieve the initial energy direction and concentration to cause a good integral bond between the pieces. In these instances, one will find the PET plastic is usually not directly molded into its final shape by an injection molding as are many other containers such as, for example, polyethylene plastic containers. Rather, the PET plastic is first injection molded into a small preform which is then blown into the final enlarged container shape. With such preforms, often it is not economically feasible to have a handle thereon to be blown into a larger size or to attach a separate handle thereto using conventional techniques. Often for larger sizes of PET containers, e.g., a three liter container, it is desirable to attach a handle for ease in pouring the contents from the container.
The present invention is also directed to applications where, heretofore, one or more plastic pieces have been secured together by metallic screws and it is desirable to eliminate the metallic screws and to secure the members together using an improved plastic fastening system. In other instances, pieces have been heat staked together and it is desired to replace heat staking of components together with a better plastic fastening system than a heat staking system.